Multiple emulsions may generally be categorized into one of two types: water-in-oil-in-water emulsions which are water continuous and oil-in-water-in-oil emulsions which are oil continuous. In each case the internal and external phases are alike and an intermediate phase separates the two like phases. The intermediate phase would normally be immiscible with the two like phases. Viewed in another way, water-in-oil-in-water multiple emulsions have a continuous external aqueous phase, in which is dispersed a lipid phase, which lipid phase has dispersed therein a internal aqueous phase. And oil-in-water-in-oil multiple emulsions have a continuous external lipid phase, in which is dispersed an aqueous phase, which aqueous phase has dispersed therein an internal lipid phase.
An important area of research concerning multiple emulsions has been directed largely to the problem of inherent instability of such systems. In the case of W/O/W emulsions, there is breakdown of the emulsion where discontinuities in the lipid phase permit the separated aqueous phases to coalesce. An analogous breakdown problem exists with O/W/O emulsions. Increasing the concentration of lipophilic emulsifier in the intermediate lipid phase of W/O/W emulsions or the concentration of hydrophilic emulsifier in the intermediate aqueous phase of O/W/O emulsions may tend to increase the integrity of the aqueous/oil interface, depending on type and amount of emulsifier employed, but notwithstanding increased concentrations of lipophilic or hydrophilic emulsifier, W/O/W and O/W/O emulsions tend to coalesce upon standing, particularly when stored at refrigerator temperatures. Moreover, increased concentrations of emulsifiers may be unacceptable for use in food emulsions and pharmaceutical delivery applications, where such concerns as off-flavors caused by emulsifiers, or FDA regulations, pragmatically limit the type and concentration of emulsifier which can be used. It would therefore be extremely desirable to provide multiple emulsions which are very stable to coalescence with aging and/or storage, even at refrigerator temperatures, which emulsions may be made using relatively low concentrations of emulsifiers.
With respect to food technology, considerable research effort has been expended on developing reduced fat food products which have low oil content, particularly aqueous based products which have low or substantially no fat content. Significant advances have been made in reducing fat and oil content of various food products through the use of, for example, water-in-oil emulsions or water-in-oil-in-water emulsions, wherein water occupies volume which otherwise would have been occupied with oil, thereby commensurately reducing the amount of oil in an oil-containing food product. For example, Takahashi et al., U.S. Pat. Nos. 4,632,840, 4,626,443 and 4,626,444 disclose reduced fat salad dressing having a W/O/W emulsion base. Such salad dressings nevertheless still have about 30% oil by weight. Further fat reductions have been obtained using, as fat mimetics, novel carbohydrate/protein complexes such as those disclosed in PCT International Application Publication No. WO 89/10068 or microreticulated microcrystalline cellulose as disclosed in U.S. Pat. No. 5,011,701. Such carbohydrate/protein complexes or microreticulated microcrystalline cellulose are particularly useful in providing no-fat food products such as viscous and pourable salad dressings and the like having fat-like organoleptic characteristics.
While elimination or substantial reduction of oil content is attainable, such low-fat or no-fat products characteristically lack (or lose during storage) the desirable flavor perception possessed by their high-fat counterparts. Stabilization of aqueous soluble or lipid soluble flavors in low- or no-fat, aqueous-based food products has not received much attention. Heretofore, aqueous soluble flavors have merely been added along with other aqueous soluble ingredients to produce low- or no-fat food products; with respect to reintroducing fat-soluble flavors to reduced-fat products, Singer, PCT International Application Publication WO 90/00354 discloses adding to such low-fat and no-fat foods fat globules containing concentrated fat soluble flavoring to simulate the organoleptic affect of fat-rich food products. In each of these cases the flavors are in contact with the aqueous-based food vehicle environment (either directly or at the interface between the fat globules and the aqueous base of the food vehicle) and thereby may be adversely affected. Flavor perception in low- or no-fat food products containing soluble flavors simply mixed into the aqueous-based food vehicle, e.g. viscous or pourable salad dressings or the like, rapidly deteriorates presumably due to interaction of flavors with the aqueous base, giving such products a short shelf life. It would therefore be desirable to provide aqueous-based food products (especially no-fat products) which have aqueous or oil soluble flavor components stably maintained so as to protect the flavors from volatilization, oxidation and other undesirable events, during extended storage, while at the same time providing for ready release of such flavors, with good organoleptic characteristics, when such low/no-fat food products are eaten.
In view of the above, it is an object of the present invention to provide very stable W/O/W and O/W/O multiple emulsions which utilize reduced amounts of emulsifiers, which multiple emulsions are suitable for food emulsion technology, as well as other applications utilizing multiple emulsions. It is also an object of the present invention to provide flavor-delivering compositions which are stably maintained in low-fat or no-fat products, such that the flavors are protected from the aqueous-based food vehicle environment until the food product is eaten, whereupon the flavor is readily released to yield a desirable taste perception and mouthfeel. These and other objects of the invention will become apparent from the following detailed description.